Atrial repolarization as observable during the PQ interval

ObjectiveWe aimed to study the involvement of atrial repolarization in body surface potentials.MethodsElectrocardiograms of healthy subjects were recorded using a 64-lead system. The data analysis focused on the PQ intervals while devoting special attention to the low-amplitude signals during the PQ segment: the segment from the end of the P wave until onset QRS. The data were analyzed by inspecting body surface potential maps and the XYZ signals of the vectorcardiogram.ResultsStandard P-wave features exhibited normal values. The local potential extremes were found at positions not sampled by the standard leads. The PQ segment was found to be not isoelectric, the time course of the potential distribution being very similar to that during the P wave but for a reversed polarity and about 3-fold lower magnitudes.ConclusionThe results demonstrate a significant involvement of atrial repolarization during the PQ interval and essentially discordant “atrial T waves,” suggesting a small dispersion of atrial action potential durations.